A device for inoculating a fluid conducted through pipes is described in DE 1 242 575 A1. The device is used to inoculate water flowing, e.g., through the piping of a water supply system. The device has a reservoir of the flexible bag type, filled with inoculant. In order to transport the inoculant from the reservoir, the device uses the energy of the water's flow. For this purpose, a throttle plate is incorporated into the cross-section of the pipe through which the water flows. However, the throttle plate narrows the pipe's cross-section. This favors deposits in the throttle plate area, which interrupt the transport mechanism for the inoculant, having a negative impact on the function of the device.